Wildlife Monographs

Determinants of Breeding Distributions of Ducks

Results

Breeding Distributions of the Species

American Wigeon.—This species reached high densities in the
southern prairie provinces but was often abundant in the north as well (Fig.
6A). Wigeon were uncommon south of Canada. Within prairie and parkland habitats,
densities steadily declined away from the area of highest density, much like
the mallard and gadwall. Wigeon winter throughout the southern United States,
along the Yucatan Peninsula of Mexico, and in the Caribbean. Numbers of spring
arrivals using the southern corridors probably slightly outnumber those entering
from the southwest (Bellrose 1980). An additional few may migrate to breeding
grounds in the parklands directly from wintering locations in the Middle Atlantic
States (Bellrose 1980).

Figure 6. (A) Average species density by stratum, 1955-81;
(B) correlation between species density and local pond counts, 1955-81; and
(C) correlation between species density and total pond counts, 1955-81.

Wigeon densities generally did not correlate closely with local pond densities
(Table 3). The highest correlations between wigeons
and local ponds were in western South Dakota and in the southwestern part of the
prairie provinces (Fig. 6B). This pattern is consistent with the large migration
of wigeon through the western portal. Higher correlation coefficients between
wigeon and ponds were associated with strata with high densities of the species,
except that wigeon were common in 3 parkland strata in Alberta and Saskatchewan,
but correlations there were low.

Wigeon densities correlated positively with total ponds in many strata of
the central portion of its range (Fig. 6C). They were negatively associated
in many strata, particularly those on the eastern edge of its range and in the
north.

The few appreciable correlations between wigeon numbers and ponds were in
the southwestern portion of their range, mostly south of the area of highest
densities. When total pond numbers were high, wigeon densities were depressed
not only in many strata in the north, but also in several along the eastern
edge, suggesting drought displacement both northward and eastward. The limited
evidence suggests fairly strong homing by the species (Table
4). We suggest that wigeon arrive on their breeding grounds from the south
and the southwest; many remain in strata initially encountered if pond conditions
there are satisfactory (thus accounting for the high correlations with ponds
there); otherwise they overfly to the north and east.